The invention relates to apparatus for removing carbon monoxide carbon dioxide and other impurities from hydrogen produced for a fuel cell by catalytic reforming of hydrocarbon fractions or alcohols.
Ongoing research for fuel-cell power generators has undertaken the use of bottled propane, commercially available methanol or other hydrocarbon fractions, such as methane as a source of hydrogen for fueling proton fuel cells. Methane, propane, other hydrocarbons or methanol are suitable for producing hydrogen through a catalytic steam reformer which lends itself to packaging in a system for portable fuel-cell power generation aboard recreational vehicles (RVs) as described in U.S. Pat. No. 6,352,792 titled PORTABLE COGENERATION FUEL-CELL POWER GENERATOR FOR RECREATIONAL VEHICLES filed Mar. 17, 2000, which can also be used for stationary applications.
Such RV power generation systems, and other system applications, utilize hydrogen for proton fuel cells because hydrocarbon fuel or alcohol is readily available as a source of hydrogen. The problem is that, along with a hydrogen-rich gas produced by a reformer, carbon monoxide and other contaminants are produced in the outgoing gas. It is extremely important that hydrogen entering a fuel cell be clean and free of carbon monoxide and other contaminants which can be expected to reduce fuel cell life and efficiency.
Measures have been taken by others to remove carbon monoxide, such as selective oxidation of CO in the presence of hydrogen. Others use a conventional metallic membrane to purify hydrogen, but purification is not 100%, so they also require the use of a methanation catalyst which catalyzes the conversion of CO to methane (CH4). It is not known what effects prolonged exposure to methane will have on fuel cells. It would therefore be preferable to use selective oxidation of CO, but then the presence of CO2 in the hydrogen gas would be increased along with some other concerns. Therefore, it would be preferable to remove virtually all contaminants from the hydrogen gas in the stream from the hydrocarbon or alcohol reformer to the fuel cell by filtration alone.
In accordance with the present invention, a purifier for hydrogen rich gas from a hydrocarbon or alcohol reformer comprises a semipermeable metallic membrane employed to purify output hydrogen gas before it reaches the fuel cell. The membrane is wrapped around a first tubular support member made from a sheet of metal mesh or screen, or from a perforated section of a tube, and placed within a second tubular support member similarly made but slightly larger, such as by having a slightly larger diameter in the case of a tubular support member, thereby sandwiching the membrane between support members. The support members are preferably made of stainless steel and welded together at their ends to form a seal for the membrane in the assembly such that no gas may pass around the membrane, only hydrogen through the membrane.
The welded membrane assembly is encapsulated in a closed chamber having an input tube at one end for introducing hydrogen rich gas from a source to one end of the encapsulated tubular membrane assembly. The hydrogen is then purified by filtration through the membrane assembly into the outer, sealed chamber. An output tube is located at the other end of the tubular membrane assembly to carry away the gas that does not pass through the membrane. An outside tube connected to a port in the sealed chamber directs the purified hydrogen to fuel cells.
A proportional valve in the output tube maintains constant pressure inside the welded membrane assembly. A directional valve downstream from the proportional valve is provided to recycle contaminated gas from the output tubular member of the chamber back to the input tubular member for further filtering or out to a burner for generating steam for the catalytic reformer that provides the hydrogen-rich gas to the purifier.
The first and second tubular members, and the chamber as well, may be of any geometric cross-sectional shape, such as circular, elliptical, rectangular or some other shape, but a circular shape shown in the drawings is preferable. In any case, the novel features that are considered characteristic of this invention are set forth with particularity in the appended claims.
Should the membrane employed prove not to be 100% efficient, any remaining contaminants in the hydrogen gas from the membrane assembly may be further filtered out in a second membrane assembly like the first, except that it could require its residual contaminated gas output to be always recirculated through a proportional valve because it is virtually free of any hydrogen. The invention will best be understood from the following description when read in connection with the accompanying drawings.